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Given a string, find the longest substring that contains only two unique characters. For example, given "abcbbbbcccbdddadacb", the longest substring that contains k unique character is "bcbbbbcccb".
分析：
用hashmap记录每个character从start到当前位置出现的次数，如果第k + 1个character出现, 更新maxLength，我们需要把左边的pointer(start) 往右移，直到从start到current之间只有K个character.
1 public class Solution { 2 public int lengthOfLongestSubstringKDistinct(String s, int k) { 3 if (k == 0 || s == null || s.length() == 0) return 0; 4 if (s.length() <= k) return s.length(); 5 6 HashMap<Character, Integer> map = new HashMap<Character, Integer>(); 7 8 int maxLen = k; 9 int start = 0; 10 for (int i = 0; i < s.length(); i++) { 11 char c = s.charAt(i); 12 map.put(c, map.getOrDefault(c, 0) + 1); 13 if (map.size() > k) { 14 maxLen = Math.max(maxLen, i - start); 15 while (map.size() > k) { 16 char preCh = s.charAt(start); 17 if (map.get(preCh) == 1) { 18 map.remove(preCh); 19 } else { 20 map.put(preCh, map.get(preCh) - 1); 21 } 22 start++; 23 } 24 } 25 } 26 maxLen = Math.max(maxLen, s.length() - start); 27 return maxLen; 28 } 29 }
Longest Substring with At Most K Distinct Characters
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原文地址：http://www.cnblogs.com/beiyeqingteng/p/5731307.html
